在 Objective-C 中将 NSArray 过滤为新的 NSArray [英] filtering NSArray into a new NSArray in Objective-C

问题描述

我有一个 NSArray，我想用原始数组中满足特定条件的对象创建一个新的 NSArray.标准由返回 BOOL 的函数决定.

I have an NSArray and I'd like to create a new NSArray with objects from the original array that meet certain criteria. The criteria is decided by a function that returns a BOOL.

我可以创建一个 NSMutableArray，遍历源数组并复制过滤器函数接受的对象，然后创建它的不可变版本.

I can create an NSMutableArray, iterate through the source array and copy over the objects that the filter function accepts and then create an immutable version of it.

有更好的方法吗?

推荐答案

NSArray 和 NSMutableArray 提供了过滤数组内容的方法.NSArray 提供了 filteredArrayUsingPredicate:，它返回一个新数组，该数组包含接收器中与指定谓词匹配的对象.NSMutableArray 添加了 filterUsingPredicate:，它根据指定的谓词评估接收者的内容，只留下匹配的对象.以下示例说明了这些方法.

NSArray and NSMutableArray provide methods to filter array contents. NSArray provides filteredArrayUsingPredicate: which returns a new array containing objects in the receiver that match the specified predicate. NSMutableArray adds filterUsingPredicate: which evaluates the receiver’s content against the specified predicate and leaves only objects that match. These methods are illustrated in the following example.

NSMutableArray *array =
    [NSMutableArray arrayWithObjects:@"Bill", @"Ben", @"Chris", @"Melissa", nil];

NSPredicate *bPredicate =
    [NSPredicate predicateWithFormat:@"SELF beginswith[c] 'b'"];
NSArray *beginWithB =
    [array filteredArrayUsingPredicate:bPredicate];
// beginWithB contains { @"Bill", @"Ben" }.

NSPredicate *sPredicate =
    [NSPredicate predicateWithFormat:@"SELF contains[c] 's'"];
[array filteredArrayUsingPredicate:sPredicate];
// array now contains { @"Chris", @"Melissa" }

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